[llvm-dev] warnings and error messages always go to standard error

[Geoff Levner via llvm-dev]

Greeting, LLVM wizards,

We are using Clang and LLVM in an application to compile and execute C++
code on the fly. If the code fails to compile, I would like to be able to
pop up a dialog box telling the user why. But warnings and error messages
go straight to standard error.

I have tried passing a raw_string_stream to TextDiagnosticPrinter instead
of errs(), but that seems to have no effect. What is that stream actually
used for? Am I doing something wrong? I have attached the code we use to
compile (simplified a bit).

Thanks,
Geoff


    IntrusiveRefCntPtr<DiagnosticOptions> diag_opts(new DiagnosticOptions);
    std::string diagnostics;
    raw_string_ostream diag_stream(diagnostics);
    TextDiagnosticPrinter *diag_client =
        new TextDiagnosticPrinter(diag_stream, diag_opts.get());
    IntrusiveRefCntPtr<DiagnosticIDs> diag_ids(new DiagnosticIDs);
    DiagnosticsEngine diags(diag_ids, diag_opts.get(), diag_client);
    Driver driver(executable, llvm::sys::getDefaultTargetTriple(), diags);

    SmallVector<const char*, 16> args;
    // various arguments...

    std::unique_ptr<Compilation> compilation(driver.BuildCompilation(args));
    const JobList& jobs = compilation->getJobs();
    const Command& cmd = llvm::cast<Command>(*jobs.begin());
    const ArgStringList& ccargs = cmd.getArguments();
    std::unique_ptr<CompilerInvocation> invocation(new CompilerInvocation);
    CompilerInvocation::CreateFromArgs(
        *invocation,
        const_cast<const char**>(ccargs.data()),
        const_cast<const char**>(ccargs.data()) + ccargs.size(),
        diags);

    CompilerInstance clang;
    clang.setInvocation(std::move(invocation));
    clang.createDiagnostics();

    std::unique_ptr<CodeGenAction> action(
        new EmitLLVMOnlyAction(&my_llvm_context));
    if (!clang.ExecuteAction(*action)) {
        if (diag_stream.str().empty()) {
            setError("Compilation failed: see standard error for details.");
        } else {
            setError("Compilation failed:\n" + diag_stream.str());
        }
    }
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